This issue is typically related to the Windows 10 Credential Manager as well as the way your network sharing settings are configured. Here are some steps you could follow to troubleshoot:
1. **Check Sharing Settings**: Ensure both computers are in the same workgroup. You can check this by right-clicking on 'This PC', selecting 'Properties', and viewing 'Computer name, domain, and workgroup settings'. If not, adjust the settings to match each other.
2. **Credential Manager**: On the Windows 10 machine, go to Control Panel > User Accounts > Credential Manager. Here, you need to remove Windows credentials related to the Windows 7 machine. Then, try to access the Windows 7 shared drive again, it should prompt for the username and password. Here, ensure you enter the full username like this : `<Windows7PCname>\<username>`.
3. **Network Settings**: On your Windows 10 computer, try to set the advanced network settings to the same as that on the Windows 7. Go to Control Panel -> Network and Internet -> Network and Sharing Center -> Change advanced sharing settings. Especially, Turn off password-protected sharing if it was on.
4. **Registry Tweak**: Sometimes Windows 10 restricts the use of older versions of the SMB protocol that Windows 7 uses for shared folders. You may need to enable SMB 1.0/CIFS File Sharing Support in 'Windows Features' on your Windows 10 machine.
Remember, the username for the shared resource is the one set on the Windows 7 computer. Also, make sure the user account on the Windows 7 machine has a password, as Windows restricts remote users in case of blank passwords.
Also, mixing different Windows versions in a network setting isn't always seamless. If these steps don't resolve the issue, consider upgrading the Windows 7 machine to ensure compatibility or use a more centralized network storage solution. This will help in long-term maintenance, security, and general use.
Let us know if you need more help!
